The human immunodeficiency virus (HIV) is the etiologic agent of AIDS> It is estimated that at least 2 million individuals are presently infected with HIV in the United States alone and most are expected to develop AIDS. Since there is currently no completely effective drug for treating AIDS, and since no vaccine exists to prevent HIV infection, AIDS clearly remains a major health problem. HIV encodes several regulatory proteins that are not found in simpler retroviruses. One of these proteins, tat is a powerful activator of HIV gene expression and is essential for HIV replication. Tat provides a good target for an anti-AIDS drug since inhibitors of tat would be expected to block HIV replication or prevent induction of virus from its latent state. Although such drugs would not eliminate infection by HIV, they may prevent or slow down the progression from asymptomatic infection to clinical AIDS. To design a drug directed against tat, it will be important to understand more about the structure and function of tat. We have previously shown that purified tat can form metal-linked dimers in vitro. This application describes experiments designed to determine what the active form of the tat protein is and how metal-binding may be involved in tat function. The unusual cysteine-rich metal-binding may be involved in tat function. The unusual cysteine-rich metal-binding region may provide a particularly susceptible target for inactivation. We have also shown that the tat protein can be taken up by cells grown in tissue culture and activate the viral promoter. Experiments to determine the significance of cellular uptake of tat for the progression of AIDS and for escape from HIV latency are proposed. Potential inhibitors of transactivation and cellular uptake will be tested using assays described in this application. Possible inhibitors include anti-tat antibodies, peptides from tat which might compete for dimerization or other tat-protein or tat-nucleic acid interactions, chelating agents and other compounds directed against the metal-binding sites, and compounds directed against the basic region. Experiments have been designed to answer basic questions about tat activity while at the same time testing new strategies for tat inhibition.